LW-MW-SW Relay Tuned 15' Noise Reducing Vertical Antenna

Useful information regarding antennas for SDR products.
vk7jj
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Location: Tasmania

Re: LW-MW-SW Relay Tuned 15' Noise Reducing Vertical Antenna

Post by vk7jj » Wed Jul 10, 2019 3:18 am

sdrom33 wrote:Hi Phil,

<snip> Far from being offended, but really thrilled, I understand the problems with the TCM exercise: it is not small, has no gain and is more susceptible to noise intake than other antennas. You wrote about a "small" 20 m loop, but how small is small? May I ask you to expand a little on this antenna? What would happen should I wish to use it on 40 m as well?
Hi Thomas, it's sad that the level of man made noise where most of us live means really neat antennas like the TCM are less rewarding to use.

Don't know if you've ever read much by Cebik on antennas, he was my hero, I've modelled and built and used dozens of his antennas over the years. When it came to simple and effective HF antennas he wasn't all that excited by large wire loops as he considered using them mostly on their fundamental frequencies where they primarily used for NVIS. Plus his focus was both Tx and Rx on the ham bands which is quite different from todays renewed interest in wide band listening that has blossomed with SDR devices.

His work is absolutely marvellous though and makes great reading, it used to be behind a paywall until recently:

http://www.antentop.org/w4rnl.001/radio.html

Large wire loops here; there are other articles about them too but this should answer a lot of your questions:

http://www.antentop.org/w4rnl.001/atl1.html

--
You wrote about a "small" 20 m loop, but how small is small? May I ask you to expand a little on this antenna? What would happen should I wish to use it on 40 m as well?
A "large" wire loop as opposed to a compact HF loop is simply the largest area you can accomodate within your backyard's limitations using a wire. Making it delta shaped reduces the remote mounting points to two and causes it to be more omnidirectional than a geometric square "quad" shape.

For best performance on the ham bands, because of their harmonic relationship, choose a total wire length that is equal to one wavelength on the lowest frequency you'd like to work on. Eg. resonance on 3.55MHz would ensure that the loop has as low a reactance and return loss as possible on 7.1MHz, 10.65MHz, 14.2MHz, 17.75MHz, 21.3MHz, 24.85MHz, 28.4MHz and so on.

On other frequencies regardless of resonance you just accept whatever characteristics your backyard causes your loop to have, in the same way we accept the limitations of so-called long wires and whatever. There is a key difference with the large loop though, they tend to have a very much more even impedance and low reactance compared to non loops, with the added very marked advantage of lower noise / balanced feedline.

There has in the past been much debate about whether loops are somehow more immune to noise than non-loops; all I can say is that at my location there is no comparison at all, all my many many best efforts with very long wires, really well built and sited inverted L antennas (a favourite of Cebik) and even dipoles have resulted in incurable and pretty much unworkable noise. Travelling outback Australia is the only place I've found that inverted Ls and verticals really come into their own, and I've done that extensively for two years living in a 4WD truck, modelling and dreaming antennas all the way.

Bottom line: try it, if it doesn't work out for you then hopefully you don't have the means to fly over here and strangle me.

Regards, Phil

BTW, these are of an older loop taken some time ago before Steve Andrew's beaut spectrum analyser software, at least you can see how you don't get unworkable high impedances on even harmonics like you do on everything else.

Together these pics cover 1.8MHz and up.
HP2-1-8.png
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vk7jj
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Location: Tasmania

Re: LW-MW-SW Relay Tuned 15' Noise Reducing Vertical Antenna

Post by vk7jj » Wed Jul 10, 2019 3:37 am

glovisol wrote:Hi Phil,
I AM SIMPLY AMAZED!!
What a skeptic!!

Hi Gianfranco, good on you. How rewarding! There surely is no silver bullet though, no single solution, there are no miracles and no free lunches!

Regards,

Phil

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Paul
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Location: SW UK

Re: LW-MW-SW Relay Tuned 15' Noise Reducing Vertical Antenna

Post by Paul » Wed Jul 10, 2019 5:33 am

Just off to find an abandoned pallet......

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glovisol
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Location: Piedmont, Italy

Re: LW-MW-SW Relay Tuned 15' Noise Reducing Vertical Antenna

Post by glovisol » Wed Jul 10, 2019 9:52 am

Paul, I will be very glad to hear about your experience with this simple antenna. The only important thing for success must be elevation and in this my setup is OK, because I am three storeys high, or up about 16 m. Superior performance is with the antenna in horizontal position. In vertical position I suppose the wall behind it is cutting most signals off.

I tried this again this morning, just to be sure I had not dreamed. The low noise ferrite transformer is essential. If I connect the two conductors directly to the HI Z input I get a very high noise level and no signals. This is the transformer I use at home with the Beverage, surely not optimal for this setup.

Toroid core: FT-37-43 (material type 43)
Ext. dia.: 0.375"
Internal dia.: 0.187"
Thickness: 0.125"
PRIMARY:6 turns enamel copper wire 0.5 mm dia.
SECONDARY: 2 turns enamel copper wire 0.5 mm dia.
PRI & SEC MUST NOT OVERLAP but be as far separate as possible.

I hope Phil will read this and tell me what impedance I should expect from this marvel.

Pics were taken yesterday evening at 22:00 local time.

Share your experience, please!

Gianfranco
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glovisol
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Re: LW-MW-SW Relay Tuned 15' Noise Reducing Vertical Antenna

Post by glovisol » Wed Jul 10, 2019 10:02 am

Phil,

It is really rewarding to have around a guy like you. Nothing can substitute experience and your experience in antennas is a great gift to all of our Community Forum. Will surely pester you in August, when I come back. looking forward to setting up this giant square!

Gianfranco

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sdrom33
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Re: LW-MW-SW Relay Tuned 15' Noise Reducing Vertical Antenna

Post by sdrom33 » Wed Jul 10, 2019 10:56 am

Phil,

Thanks a lot for your help & guidance. I am studying the references, got a lot to learn in practical antennaship & will get back to you when stronger on my legs. Seems glovisol is having a ball with your concepts!

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glovisol
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Re: LW-MW-SW Relay Tuned 15' Noise Reducing Vertical Antenna

Post by glovisol » Wed Jul 10, 2019 12:40 pm

IMPORTANT

Paul I have discovered that I have the best performance using the HI Z input, as I have been doing since yesterday evening and using the following low noise transformer:

Toroid core: FT-37-43 (material type 43)
Ext. dia.: 0.375"
Internal dia.: 0.187"
Thickness: 0.125"
PRIMARY:5 turns enamel copper wire 0.5 mm dia. (Zin = 450 Ohm)
SECONDARY: 7 turns enamel copper wire 0.5 mm dia. (Zout = 1 KOhm)

Thinking you had a 50 Ohm only input RSP, earlier I have given you the following data:

Toroid core: FT-37-43 (material type 43)
Ext. dia.: 0.375"
Internal dia.: 0.187"
Thickness: 0.125"
PRIMARY:6 turns enamel copper wire 0.5 mm dia. (Zin = 450 Ohm)
SECONDARY: 2 turns enamel copper wire 0.5 mm dia.(Zout = 50 Ohm)

But the 50 Ohm port loses approximately 12 dB @ 14 MHz on actual antenna signals. So if you have a HI Z input, this is the one to use.

glovisol

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Paul
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Re: LW-MW-SW Relay Tuned 15' Noise Reducing Vertical Antenna

Post by Paul » Wed Jul 10, 2019 3:29 pm

Thank you for the detailed guidance Gianfranco.
I actually have a duo and an RSP2, so OK in that respect, but need to think about elevation, the wife and how to construct the low-noise transformer (I have no history in electronics and have only used ready-made baluns before) so please excuse the obvious ignorance - I will learn - still seem to be capable at 80+....

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glovisol
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Re: LW-MW-SW Relay Tuned 15' Noise Reducing Vertical Antenna

Post by glovisol » Wed Jul 10, 2019 5:24 pm

Hi Paul,

Do not worry for the 80+, I will turn 80 in september next....so you are in good company.

Detailed instructions with pertinent photos are posted here:

https://www.sdrplay.com/community/viewt ... 9&start=20

Just patiently go over the thread until you come to the directions for building the transformer (very easy!)

Kind regards,

Gianfranco

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Paul
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Re: LW-MW-SW Relay Tuned 15' Noise Reducing Vertical Antenna

Post by Paul » Wed Jul 10, 2019 6:55 pm

Thanks again Gianfranco - Pictures ARE worth a 1,000 words!

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